p065

Takahiro Takekiyo^a, Naohiro Hatano^a, Hiroshi Abe^b andYukihiroYoshimura^a

^aDepartment of Applied Chemistry, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan
^bDepartment of Materials Science and Engineering, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan

High Pressure Research Vol. 32 (2012) 150-154.

Abstract
We have investigated the pressure-induced Raman spectral changes of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF₄]).We found that [emim][BF₄] did not crystallize up to 1.2 GPa. The Raman CH stretching spectra arising from the CH₃ groups of the ethyl-chain and the CH₃ group adjacent to the imidazolium-ring in [emim]⁺ cation largely changed against pressure. Moreover, the Raman intensity of the CH₂ (N) bending band arising from the alkyl-chain drastically changes with increasing pressure, but that of the imidazolium-ring in-plane bending band arising from the imidazolium-ring is independent of pressure. Our results show that the environment around the alkyl-chain of [emim][BF₄] is largely perturbed rather than that around the imidazolium-ring upon compression.

	Fig. 1 Optimized structures of the trans (planar) and gauche (non-planar) conformers of [emim]⁺ cation.
	Fig. 2 (a) Raman CH stretching spectra and (b) the frequency shifts of [emim][BF₄] as a function of pressure. The open triangle, closed and open circles represent the mixing band of the C(2).H, C(4).H, C(5).H ass mode of the imidazolium ring, the C(8).H ass, and C(6).H ass modes of the alkyl-chain, respectively.
	Fig. 3. (a) Raman spectra in the low frequency region of [emim][BF₄] as a function of pressure. Pressure-induced frequency shifts of (b) BF₄ stretching band, and (c) the imidazolium-ring in-plane bending and CH₂ (N) bending bands of [emim][BF₄]. The open triangle, open and closed circles represent the gauche, gauche, and trans conformers for the CCNC angle of [emim]⁺ cation, respectively.

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Last Modified: May 1, 2012